Gunmen’s ruthless tactics, which left children’s show host and a renowned poet among the dead, were advised just weeks ago by Al Qaeda’s leader.

Ayman al Zawahiri, leader of Al Qaeda, who gives messages to the world in videos, earlier this month advised jihadists to target Westerners, avoid Muslim victims and take hostages. This was the blueprint followed in the Westgate attack.

The Westgate shopping mall is popular among foreigners and wealthy Kenyans, and witnesses say the attackers called for Muslims to identify themselves, although mainly fired indiscriminately.

By late Sunday, there were reports that more than a dozen militants holding hostages were still trapped inside the Nairobi mall, as the deadly rampage continued more than 30 hours after it began.

“We’ll not negotiate with the Kenyan gov’t as long as its forces are invading our country, so reap the bitter fruits of your harvest. #Westgate,” the Shabab tweeted on an account that was later shut down Sunday.

A criminal investigation, aided by the FBI and other foreign agencies is just beginning, but already a sadly familiar portrait of how the attack was executed has emerged.

Al Shabab, the Somalia-based group that officially joined with Al Qaeda last year, claimed responsibility. They have vowed to attack for years — their threats increasing since Kenya’s military joined African Union forces in Somalia in October 2011.

A list of names identified as the attackers, which included militants from Canada, along with those from the U.S., Syria, U.K., Sweden, Russia and Finland, circulated on social media Sunday.

By evening, an email used by the Shabab to a group of journalists, including the Star, stated: “We have not mentioned anything so far regarding the names of the Mujahideen or any other details of the operation.”

But if it’s true, this is not the first time a Canadian has been at the forefront of such an assault.

In Somalia earlier this year, 29-year-old Canadian Mahad Dhore led a team of fighters in an assault on the capital’s courthouse. During a Star investigation in Mogadishu weeks later, it was clear that the attack was well-planned, with militants breaking into groups. Some survivors of the Westgate assault described details similar to what witnesses in Mogadishu told the Star.

And in Mogadishu, like Nairobi, there were warnings such an assault was imminent and there seemed little way to stop it.

That is the sad fact about the weekend attack. Westgate was long known to be vulnerable, along with other upscale shopping malls in Nairobi, or hotels popular with Westerns, which counterterrorism officials often refer to as “soft targets” for terrorists.

But is hard to imagine how any measure of security could have prevented Saturday’s attack by more than a dozen militants wielding AK-47s and grenades, who are willing to die in the attack.

Each entrance of Westgate was staffed with armed guards with handheld metal detectors – which would have been no match for the attackers. One witness told a local Nairobi newspaper that he saw attackers enter the mall through a basement parking lot.

There was also reportedly a woman among the attackers, perhaps more than one.

Again, this wouldn’t surprise those who follow the Shabab, if true. Although Al Shabab rarely uses female fighters, the group has strong female leaders, who have largely acted as recruiters and are rarely discussed.

One major figure is a Canadian woman known among jihadis and intelligence agencies as “Mama Shabab.”

All eyes will be on Kenya this week as the country recovers from the worst terrorist attack in the region since the 1998 Al Qaeda bombing of the U.S. embassy.

The horrific images will be hard to forget — this was an attack that was widely covered.

Many foreign journalists are based in Nairobi, one of Africa’s most stable cities and a good hub for access to the rest of the continent. Dramatic images and stories were immediately transmitted and for many journalists, the story became personal.

Celebrated New York Times photographer Tyler Hicks, who has extensively covered war zones around the world, was right next door to the mall picking up framed photos. Reuters’ photojournalist Goran Tomasevic, also a veteran war photographer, was nearby and went in alongside police.

From outside, Jason Straziuso, the Associated Press correspondent in Nairobi covered the story while helping a trapped friend. She escaped and as Straziuso later wrote: “As a reporter, I knew that not everyone's day ended so well.”